Damping means and methods



Feb. 4, 1958 I w.A. TIKANEN DAMPING MEANS AND METHODS Filed Nov. 2. 1953 shaman;

IN V EN TOR.

WILL/AM 4'. r/kA/vE/v,

A TTORNEK United States Patent DAMPING MEANS AND METHODS William A. Tikanen, Reseda, Califl, assignor to Genisco, Inc Los Angeles, Calif., a corporation Application November 2, 1953, Serial No. 389,706

7 Claims. (Cl. 264-1) This invention relates to means and methods for damping the responsive movements of condiiton-sensitive members. in various devices, including various instruments and control devices for detecting and indicating changes in various conditions. The invention has been initially embodied in an accelerometer for use on aircraft, guided missiles, and the like. This particular embodiment of the invention will be described in detail herein by way of example and to provide adequate guidance for those skilled in the art who may have occasion to apply the same principles for other specific damping purposes.

The invention relates to the use of a liquid such as a suitable oil for damping the movements of a conditionsensit-ive member. In this particular embodiment of the invention, the member is an acceleration-responsive mass. The liquid is formed into a thin sheet or film between an extensive side surface of the responsive mass and an adjacent fixed surface, the two surfaces extending in the general direction of the movement so that relative movement between the two surfaces is resisted by longitudinal shearing action in the intervening liquid Since the resistance afforded by the liquid film to the relative movement of the adjacent surface of the acceleration-responsive mass varies directly with the viscosity of the liquid and varies inversely with the thickness of the liquid film, it is possible to obtain a desired damping action in an environment of a given temperature by using a liquid of appropriate viscosity at the given temperature and by confining the liquid to form a film of appro priate thickness. in many installations, however, and especially in installations for aircraft and guided missiles, the operating temperature varies widely and, unfortunately, the viscosity of the liquid varies materially with the temperature changes.

The invention is directed to the problem of using a motion-damping liquid. film of this character in such manner as to obtain a substantially constant damping effect over a range of operating temperatures. In general, this problem is solved by providing means to vary the thickness of the liquid film in response to temperature changes thereby to compensate for the efiect of temperature on the viscosity of the liquid. More specially, the preferred solution for the problem is to use a temperature-responsive Wall member bounding at least" one side of the film to narrow the film-confining space automatically in response to rising temperatures. Varione wall constructions and arrangements may be used to carry out this purpose.

In the present embodiment of the invention, a bimetallic wall construction is used for this purpose. The acceleration-responsive mass is surrounded by a body of liquid and has a side wall presenting an extensive liquid-contacting surface oriented with the direction of responsive movement .of the mass. An adjacent outer wall member of bimetallic construction coroperates with the side wall of the mass to form the liquid into the desired thin film. The bimetallic wall member is fixedly ice mounted at one of its ends with its other end free to flex inward to narrow the film-confining space in response to rising temperature. Preferably suitable stop means is positioned for abutment with the free end of the bimetallic outer wall member to limit its inward flexure movement and thus prevent the outer wall memher from contacting the acceleration-responsive mass.

A certain difficulty arises in such an arrangement, however, Whenever the temperature continues to climb after the end of the outer bimetallic wall member contacts the limiting stop. The bimetallic wall member continues to flex with rising temperature and in doing so reacts against the fixed stop by bowing outward. This reverse bowing action of the outer bimetallic wall member defeats its purpose by increasing the thickness of the liquid film as the ambient temperature continues to climb. A feature of the invention in this regard is the provision of a shorter auxiliary wall member of the same bimetallic construction positioned to flex inward against the main bimetallic wall member at an intermediate point thereof. Thus, when the temperature continues to rise above a critical point at which the main bimetallic wall contacts the limiting stop, the auxiliary bimetallic wall member exerts progressively increasing pressure to oppose the bowing tendency of the main bimetallic wall member.

The invention, with its various features and advantages, will be readily understood from the following description considered with the accompanying drawing.

In the drawing, which is to be regarded as merely illustrative:

Figure l is a view of the presently preferred embodiment of the accelerometer, the view being partly in section and partly in side elevation;

Figure 2 is a sectional view taken as indicated by the broken line 2-2 of Figure 1;

Figure 3 is an enlarged fragmentary view of a portion of the accelerometer showing a potentiometer incorporated thereon; and

Figure 4 is a plan view of the potentiometer.

The accelerometer shown in the drawing includes a condition-responsive member which, in this instance, is an acceleration-responsive mass in the form of a metal body, generally designated by numeral 10 that is mounted on an upright blade 11. The blade 11 is resiliently flexible to a degree to make the arrangement sensitive to acceleration forces of a selected range of magnitude. The acceleration-responsive body It) carries an upwardly extending brush element 12 which is the movable contact of a potentiometer, generally designated by a numeral 13. The fixed structure of the device comprises a suitable sheet metal housing, generally designated 14, and a U-shaped frame 15 that is mounted in the housing by suitable screws 16.

The housing 14; comprises a sheet metal shell 20 of rectangular configuration, one wall of which is formed with ears 21 to serve as a base for mounting the device. A suitable flanged bottom wall 22 and a similar flanged top wall 23 are attached to the shell 20 by suitable means such as solder 2d. The top wall 23 carries three suitable electrical terminals 25 which are connected respectively to the two ends of the potentiometer 13 and to the brush element 12 by suitable flexible wires (not shown). The top wall 23 is also provided with a circular opening in which is mounted a threaded bushing 27 adapted to seat a suitable sealing gasket 28. The bushing 27 is united with the top Wall 23 in a fluid-tight, manner and isadapted to receive a threaded plug 30 which co-operates, with the gasket 28 to seal ofi the interior of the housing. The housing confines body of liquid 34 such as suitable oil and, if desired, the plug 3% may be soldered to the bushing 27 for permanently sealing the contents of the housing.

referably. the top wall 23 of the housing is connected with the lJ-shaped frame 15 by suitable spacer means comprising a sleeve 35 and a long screw 36. The long screw 36 extends through both the top wall 23 and the spacer sleeve 35 and is threaded into the U-shaped frame 15. With the top wall 23 assembled to the lJ-shaped frame 15 in this manner, and with the assembly out side of the shell 29, the three terminals 25 may be wired to the potentiometer and brush and the acceleration-responsive body may be mounted on the U-shaped frame by the flexible blade 11 in preparation for mounting the top wall in the sheet metal shell 20. The U-shaped frame 15 carrying the top wall may then be inserted into the shell and permanently attached thereto by the screws 16. Thus the U-shaped frame, together with the spacer sleeve and screw 36 serves as means to hold the top wall 23 in position for assembly to the shell 20 by soldering.

The vertically positioned U-shaped frame 15 has a lower leg 37 which is made in two sections. The outer section 38 serves as a clamp member for fixedly mounting the flexible blade 11 by its lower end, the outer section being secured to the rest of the U-shaped frame by suitable screws 39 that pass through the lower end of the flexible blade.

As best shown in Figure 3, the upper leg 40 of the U-shaped frame 15 is formed with a slot 44 to provide clearance for operation of the brush member 12 by the acceleration-responsive body 10. Preferably the U-shaped frame member 15 is adapted to serve as stop means to limit the range of oscillation of the body 10. The intermediate vertical upright portion of the frame member lies in the path of oscillation to serve as one stop and a second stop may be provided in the form of a short overhanging plate 45 that is mounted on the outer end of the upper frame leg 40 by suitable screws 46.

The potentiometer 13 is mounted on the upper leg 40 of the U-shaped frame 15 by a suitable bracket 47 and a base plate 48, the base plate being attached to the U- shaped frame by suitable screws 49 and the bracket, in turn, being attached to the base plate by suitable screws 50. As shown in Fig. 4, the screws 50 extend through suitable slots 51 in the bracket which permit the potentiometer to be adjusted longitudinally of the path of reciprocation of the brush member 12. The two screws 50 are accessible through the bushing 27 to permit adjustment of the potentiometer relative to the brush memher after the device is completely assembled. The bracket 47 is formed with two parallel upwardly extending arms 55 on which the resistor coil 56 of the potentiometer is mounted by a suitable screw 57 and nut 58.

The acceleration-responsive body 10 has an intermediate portion 60 of generally cylindrical configuration and is formed with two parallel side flanges or side walls 61 which provide the required extensive side surfaces for damping action by a film of the liquid 3 The cylindrical intermediate portion 69 of the body has a separable section 62 Which serves as a clamp member and is held in place by suitable screws 63.

The clamp member 62 cooperates with the rest of the body 10 for securing the body on the flexible blade 11 and also for gripping the stem of a T-shaped member 64. The T-shaped member 64 which is made of nonconducting material seats in a socket 65 in the body 10 to support a brush holder 68. The brush holder 68 is a suitable triangular sheet metal member mounted on the T-shaped member 64 by rivets 69 and is formed at its upper end into a split sleeve 70 in which the brush member 12 is mounted. The brush holder 68 may be formed with a suitable apertured car 71 to serve as a terminal for connecting the brush member 12 with one of the external terminals 25.

Mounted on each side of the U-shaped frame 15 by suitable screws 73 are two bimetallic wall members 74 which are positioned closely adjacent the side walls 61 of the body 10 to form the desired narrow space for a film of the liquid 34. The upper leg 40 of the U-shaped frame member serves as a stop to limit inward fiexure of the upper ends of the two bimetallic wall members 74, as may be seen in Figure l, and the side walls 61 of the body 10 are set inward from the limit positions of the two bimetallic wall members in accord with the desired minimum thickness of the two liquid films.

At relatively low temperatures, the two bimetallic wall members 74 are flexed outward from their limit positions thus providing for relatively thick films of the liquid 34 adjacent the two side walls 61 of the acceleration-responsive body 10. With rising temperature, the two bimetallic wall members 74 flex inward to reduce the thickness of the two liquid films in compensation for the decreasing viscosity of the liquid.

In those installations where the range of temperature variation does not exceed the point at which the two bimetallic wall members 74 flex inward to their inner limit positions, additional auxiliary bimetallic members are unnecessary. In the present embodiment of the invention, however, it is anticipated that the range of operating temperatures will exceed the temperature at which the bimetallic wall members 74 flex into contact with the upper frame leg 40 and, therefore, two auxiliary bimetallic members 77 are mounted against the outer sides of the bimetallic wail members 74 by the same screws 73.

The auxiliary bimetallic members 77 are substantially shorter than the bimetallic wall members 74 so that the upper ends of the auxiliary members press inward against the longer bimetallic wall members 74 at intermediate points thereof. With increasing temperature the bimetal lic wall members 74 tend to bow outward after contacting the stops, but are prevented from doing so by the inward pressure exerted by the shorter auxiliary bimetal members 77. By making the shorter auxiliary bimetallic members inherently much more powerful than the longer bimetallic wall members 74, automatic compensation for decreasing viscosity of the liquid may actually be continued above the critical temperature at which the upper ends of the bimetal wall members reach their stop positions, the continued compensation for lowering viscosity of the liquid being achieved by the auxiliary bimetal members 77 actually forcing the bimetal wall members 74 to bow inwardly for further decrease in the thickness of the liquid film.

It is apparent from the foregoing description that the extensive areas of the bimetal wall members 74 cause the formation of extensive liquid films in contact with the extensive areas of the body side walls 61 to provide the desired damping action, and that the temperatureresponsiveness of the bimetallic walls on the outer sides of the two liquid films results in the thickness of the films changing automatically to compensate for changes in the viscosity of the liquid. If the liquid employed for the damping function is a relatively light instrument oil, the described construction may be dimensioned and arranged to provide liquid films that will automatically vary in thickness, say, from a dimension of the order of magnitude of .030 inch at the low end of the range of operating temperatures to a minimum thickness of the order of magnitude of .002 inch at the upper end of the temperature scale. It will be apparent to those skilled in the art that in various practices of the invention, liquids of various viscosity may be used, the areas of the coacting film-confining surfaces may be varied, and the thickness of the films may be varied.

My description in specific detail of the presently preferred embodiment of the invention as an accelerometer will suggest to those skilled in the art various changes, substitutions and other departures from my disclosure that properly lie within the spirit and scope of the appended claims.

I claim:

1. In a condition-responsive device having a sensitive means mounted for movement in response to change of condition, the combination therewith of means to damp the movements thereof, said means including: at least one wall carried by said sensitive means for movement therewith, said wall being oriented with the direction of movement; a body of liquid submerging at least a portion of the surface of said wall; a second fixed wall separate from said member, said second wall being positioned closely adjacent said first wall to form said liquid into a film between the two walls for opposing the movement of the first wall by the resistance in shear of the film, at least one of said two walls being bimetallic to vary said space in response to changes in temperature of the liquid thereby to compensate for changes in viscosity of the liquid; stop means to limit the inward flexure of said bimetallic wall; and auxiliary bimetallic means to press inward on said bimetallic wall to oppose outward bowing of the bimetallic wall in reaction to the pressure of the bimetallic wall against said stop means.

2. In a condition-responsive device having a sensitive means mounted for movement in response to change of condition, the combination therewith of means to damp the movements thereof, said means including: at least one wall carried by said sensitive means for movement therewith, said wall being oriented with the direction of movement; a body of liquid submerging at least a portion of the surface of said wall; a second wall fixed separate from said member, said second wall being positioned closely adjacent said first wall to form said liquid into a film between the two walls for opposing movement of the first wall by the resistance in shear of the film, one of said two walls being mounted by one of its ends with freedom for movement of its other end and being of temperature-sensitive construction to flex towards the other wall in response to rising temperature thereby to narrow said space to compensate for change in viscosity of said liquid; stop means for contact by the free end of said one wall to limit flexure of said one wall towards said other wall; and temperature-responsive means to oppose outward bowing of said one wall when flexure thereof is opposed by said stop means.

3. A combination as set forth in claim 2 in which i tion responsive movement in a direction in a plane normal to said support member, said mass having two parallel side surfaces in planes parallel with said plane; a body of liquid surrounding said mass and submerging at least portions of said two side surfaces; two fixed outer walls, each positioned closely adjacent one of said side surfaces to co-operate therewith to form said liquid into film for resistance to movement of the side surface, said two outer walls being of temperature-responsive construction to vary the thickness of said films in response to changes in temperature of the liquid thereby to compensate for changes in viscosity of the liquid; stop means to limit inward fiexure of said bimetallic walls; and temperature-responsive means to oppose the tendency of the bimetallic walls to bow outward after the walls contact said stop means.

5. A combination as set forth in claim 4 in which each of said auxiliary means comprises a bimetallic member having a free end positioned to flex against the corresponding outer wall at an intermediate point thereon.

6. An accelerometer having in combination: a body for response to acceleration forces, said body having opposite parallel planar faces; a flexible blade carrying said body, said blade being rigidly fixed at one end to seek a neutral position and to flex in opposite directions from the neutral position to confine the movement of said body to a predetermined path in response to acceleration forces with the center of gravity of the body following an armate path in a plane parallel with said face and perpendicular to said blade; means to detect flexure of said blade from its neutral position; a housing enclosing said blade and body; a body of fluid in said housing submerging said body and blade to damp oscillations thereof; two wall members in said housing, each parallel with and adjacent to one of said planar faces and forming therewith a relatively narrow space filled with said liquid for damping action on said planar faces, each of said wall members being mounted with freedom to flex and being of bimetallic construction to flex inward in response to rising temperature thereby to narrow the corresponding narrow space to compensate for changes in viscosity of the liquid; stop means for contact by said wall members to limit inward fiexure of the wall members toward said planar faces; and temperature-responsive means to oppose outward bowing of each of said wall members when flexure thereof is opposed by said stop means.

7. A combination as set forth in claim 6, in which said temperature-responsive means comprises two additional bimetallic members positioned adjacent said wall members respectively, each of said additional members having a free end positioned to flex against the corresponding wall member at an intermediate point thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,084,561 Prescott et a1. June 22, 1937 2,308,582 Beale Jan. 19, 1943 2,332,994 Draper et al Oct. 26, 1943 2,552,722 King May 15, 1951 2,569,311 Hoare et al Sept. 25, 1951 

